This invention relates to an improved process for the recovery of oil from subterranean oil bearing formations which may also contain highly saline and/or hard water, e.g. water containing appreciable quantities of sodium chloride and/or water soluble salts of divalent cations such as calcium or magnesium.
The petroleum industry has long recognized that a large portion of the original oil in place in many oil-bearing subterranean formations remains in place after so-called primary oil recovery by the natural pressures of the reservoir. Waterflooding, secondary oil recovery, is routinely used to supplement the oil recovery and increase the amount of oil produced from a reservoir. Frequently, even after secondary oil recovery processes, over one-half of the oil originally present remains trapped in the formation. The addition of chemicals called surfactants to the water flooding process has been proposed as a tertiary oil recovery method to recover additional oil from the formation. Surfactants, when added to the waterflood, lower the interfacial tension between oil and water and mobilize the oil for displacement to the production well. As oil reserves dwindle and exploration for new discoveries becomes more difficult and costly, the use of improved tertiary recovery methods on previously discovered resources will play an increasingly important role in the overall production of crude oil.
Three characteristics of reservoirs, temperature, total dissolved solids (salinity), and oil type can be considerably different in each reservoir. It is known that the ability of surfactants to lower interfacial tensions and thus recover oil are very dependent on these parameters. The effectiveness of a surfactant in a given reservoir is related to its chemical structure and therefore many surfactants have been proposed for tertiary oil recovery applications.
U.S. Pat. No. 4,293,428 discloses the use of a waterflooding technique with surfactants chosen from sulfates, sulfonates, phosphates, or carboxylates to control interfacial tension.
U.S. Pat. No. 4,465,602 discloses a chemical flooding process using an alkylarylpolyalkoxyalkylene sulfonate alone or in combination with a water-soluble petroleum sulfonate as surfactants to control interfacial tension in high salinity environments.
British Pat. No. 2,156,406 discloses the use of surfactant concentrates comprising a low molecular weight sulfonate, two different alkyl aromatic alkoxy alkylene sulfonates and a carrier.
One of the major problems encountered by many surfactants is their loss of effectiveness in high salinity environments. Thus new surfactants are constantly being sought which can be effective in a range of salinity conditions.